OSC is a protocol for sending information between musical devices, over a network.
Unlike MIDI, which is defined as a stream of bytes with specific meanings, OSC
messages are human-readable text strings with no predefined meanings. It is
entirely up to individual musical devices to define what specific messages mean and
when those messages are sent.

For two devices to work together (such as REAPER an and OSC control surface
device), the user must configure one or both devices to send and receive messages
that have meaning for the other device.

OSC-capable components include hardware control surfaces, standalone computer applications,
apps for tablets and smartphones, and so on. In addition, there are middleware applications
that can convert between OSC and MIDI, so that OSC can be used for 2-way communication with
any MIDI-capable component, including almost any hardware control surface.

To enable network communication between REAPER and an OSC device, go to Options/Preferences/Control Surfaces,
and add a new OSC control surface. REAPER can receive messages from the device, send messages to the device,
or both.

To use an OSC device for basic one-way control input, enable "allow binding messages to REAPER actions and FX learn".
This will permit OSC messages from this device to be used as action shortcuts and FX parameter learn mappings,
just like any keyboard or MIDI control input.

To use an OSC device for more than basic action shortcuts and FX parameter learn, you will need
to configure either REAPER or the device to define the OSC messages that will be used for communication.

The pattern config file (.ReaperOSC) is how REAPER defines the OSC messages it understands.
In order to use REAPER with any OSC device, you can either create a custom pattern config file
so that REAPER sends and receives messages the OSC device understands, or configure the OSC device
to send and receive messages that REAPER understands, or both.

To open the default pattern config file folder, select "open config directory" under "pattern config"
in the OSC control surface settings dialog. The best way to create a new pattern config
is to make a copy of the included Default.ReaperOSC file, rename the copy, and change the patterns
defined in the file. Please see the extensive comments in Default.ReaperOSC for more detail about
how messages are formed, and what the messages mean.